Plug fuse



April 2, 1935. MlLLER'ET AL 1,996,432

PLUG FUSE Filed Jan. 3, 1955 f6 Jizzwiuiw dfwawrilzir 6037; fwdzwz Patented Apr. 2, 1935 UNITED STATES PATENT OFFICE PLUG FUSE Alexander Miller, Braintree, and George Goodwin, Avon, Mass, assignors to Royal Electric Company, Incorporated, Avon, Mass., a corporation of Massachusetts Application January 3, 1933, Serial No. 649,756

10 Claims. 200-130) This invention relates to electrical fuses more base I and passes out between the base I and a particularly of the plug type, although certain tubular side wall portion I of the top 2 where features of the invention are not limited to any its end, as at 8, is secured as by soldering to a particular type. conductive shell 9 which secures the base and One of the objects of the invention is to intop together. This shell has screw threads I0 5 crease the ease of detecting whether or not a formed therein for engaging mating portions II fuse element, has blown, of the tubular side wall 2 and through its flange A further object is to provide improved means I2, which engages beneath a rib l3 on the base for. preventing breakage of a glass top portion I, which holds the base I and the top together.

of the fuse by the impingement of hot materials The contact 4, which extends through the base I, 10 thereon when the fuse element blows. and the conductive shell 9 form two terminals A still further object is to control the venting between which the fuse element extends as in of gases from the interior of the fuse when the the usual fuse of the plug type. The fuse elefuse element blows and to cool such gases before ment portion 6 is provided as is customary with they are permitted to escape to the atmosphere. a portion I4 of reduced cross section to localize 15 Further objects and advantageous constructhe point at which rupture occurs when this eletions will appearfrom a more complete descripmentblows, and this is positioned directly back tion of certain embodiments of the invention of and adjacent to the W nd w portion 5. shown in the accompanying drawing in which It will be noted that the top 2 is provided with Figure 1 is a central longitudinal section a marginal thickened rim portion I5, which pro- 2 through a plug fuse embodying certain forms of vides means by which the plug fuse may be th i tion, grasped and turned to screw it into or out of Figures 2 and 3 are side elevations of certain the usual threaded socket formed to receive of t parts o n i Figure 1, fuses of this type. The window portion 5 is Figure 4 is a plan view of the chamber shown domed outwardly so that its outer face is brought 25 in Figure 3. outwardly beyond the plane of the outer face of Figures 5 and 6 are views similar to Figure 4, the rim I5 and the inner face of the window porbut illustrating modifications. tion 5 is formed substantially concentric to the Figure '7 is a, fragmentary view similar to a outer face in order that the thickness Of the portion of Figure 1, but showing a modification. Window Portion may be t t ly form 30 Figure 9 is perspective of d k shown i throughout. By thus extending the window por- Figure 1, tion outwardly from the rim, it is in position to Figures 8, 10 and 11 are perspectives showing catch the light and increase the illumination on further modifications. the fuse element within the receptacle so that it Figure 12 is a view similar to Figure 1 but may be more clearly visible. By forming the 35 drawn to a smaller scale and showing another window portion of substantially uniform thickmanner of indicating when the fuse element has ness throughout, no distortion of the fuse elebl ment as viewed through the window occurs.

Figure 13 is a similar view showing another Where it is attempted to form the window pormethod of decreasing the amount of hot gases tion thicker at the center to produce a magnifi- 40 when the fuse blows, cation of the fuse element, difficulties are ex- Figure 14 i a, e tion o li l4 of Figperienced, due to the fact that accurate positionure 13. ing of the fuse is necessary in order to position Referring first more particularly to Figures it in the focus of the lens thus formed, as if it is l to 4, at I is indicated a base of non-conducting not correctly positioned it is out of focus and its 45 material such as porcelain, which, together with visibility is decreased rather than increased by a top 2 of glass forms a non-conductive enclothe lens formation of the window. No such dissure within which is positioned a fuse element tortion occurs where the window is of substan- 3. This fuse element is secured at one end to tially unif thickness t ut and no exa contact 4 which extends through the base I, oeptional care in p ing the fuse element is 50 from which contact it extends upwardly from then necessarythe base I toward a window portion 5 in a closed Moreover, a concave inner face for the window end of the top 2. It extends across the receptacle portion facilitates the molding of the glass top, back of the window portion 5, as shown at 6, a rounded end to the core member which shapes 6!! and then is bent backwardly as at I! toward the the inner face of the top facilitating the molding operation and also tending to relieve the top itself from shrinkage stresses as the glass cools.

In this embodiment of the invention, it will be noted that the base i is provided with a pair of upwardly extending concentric radially spaced wall portions 2% and El between which the portion I? of the fuse element passes, and the outer portion 25 having a-perforation 25 therethrough substantially opposite to the lower edge of the top side wall portion 7? for the passage of this element. This wall portion 2E thus acts to protect the lower end portion of the side wall i from contact with hot material, such as molten 'metal' I rim i and the window portion 5 is found not liable to breakage from this cause. The inner wall 29. serves to prevent accidental contact between the'end portions of the fuse element.

"In place of attaching the outer end of the fuse element to theconductive shell 9 at its upper end as shown in Figure 1, the base may be provided with a groove as shown at 26 in Figure '7 through which the fuse element may be passed and. secured as by solder at 2? to the lower edge I seen through the window portion 5. To this end a piece of non-conductive sheet material, such as paper, may be used as shown. at 38 in Figures 1 and 9, and in order that a distinctively diiierent appearance maybe produced after the fuse blows, this disk 36 may be provided with a central opening tbimmediately back of the reduced cross section portion, E4 of the fuse elementso that when the fuse element blows-theopening 3! will be disclosed, this appearing as a dark spot at the center of the disk to. Or, if desired, this diiierence' of appearance may be further enhanced by'use of a larger opening through the disk,w;which is normally covered on its under face, as shown best in Figure 11, by sheet material 35 presenting a different color from the disk 35 and across which the fuse element portion 6 extends. Thus beforethe fuse is blown the material Sbpresents a different color adjacent to the reduced cross section portion Hi or" the fuse element. This material 35 may be secured lightly parts andthe shell 9. In order to control this venting, the confronting faces of the top and base may be-provided with channels for the'escape of the hot gases. As it is'easier to form-these 'channelsin the basal," wl'n'ch may be of porce laingthan in the top of the glass, the upper face of the base may be provided with such grooves or channels as shown at it! in Figures 3, 4 and 5, and in order to effect a better seat between the top and base, a gasket 5! may be placed therebetween. If desired, these grooves so may be made more or less tortuous to increase the surface exposed thereto and thus to produce an additional cooling eifecton these gases during their escape, as shown in Figure 6 where the grooves are made angular as shown at 53.

Other means may be used to protect the side wall of the glass top from breakage because of the impingement of hot material thereon when the fuse element blows. For example, as shown in Figure 5,instead of forming a pair of concentric wall portions such as 20 and 2 i, asshown in Figures 1, 4 and 6, a single wall portion 35 may be employed similar to the wall portion 2i, and at the side where the fuse element portion l'i passes backwardly from the window portion, this Wall 45 may be bridged by awall portion 45 so as to form with the adjacent wall portion '5? a partial enclosure for the fuse element portion I? through which it passes on its way to the perforation 48 and its passage between the'top and the base and its securement to the shell Q. This wall portion 46 prevents accidental eontactbetween opposite end portions of the'fuse element.

In place of form ng this protective element integral with the base i, it may be'formed as a portion of the sheet material forming a background for the fuse as viewed through the window. For example, as shown'in Figure 8, this sheet material piece may comprises, disk portion 5! having one or more integral wing portions 5! which may be bentdownwardly attheir juncture with the disk portion 58 and conformed to the contour'of the interior or the side walll, the fuse element portion ll of 'the'fuse element being brought, downwardly and'inwardly of the wing portion 55 which extends between it and the side wall of the glass top.

Another construction is illustrated in Figure 10 in which the sheet material background member is formedcup-shape with-a circular base portion 55 perforated at 55 ands! for the passage ofthefuse elementand having an integral skirt portion 58 formed by plaiting together the sheet materiahthis skirt portion 58 extending between the side wall of the fuse top and the fuse element. While these elementsfifl and "55, are each shown as provided with a relatively small perforation, it is of course evident that this perforation may be made larger'as shown in Figure 11, and a supplementary background element removed byblowing of the fuse element may be used if desired. In Figure 12 is shown another construction particularly intended to increase the facilitywith which a blown fuse may be detected. The space within the plug receptacle immediatelyback of thewindow' is shown as occupied by cotton or other fibrous material 69 impregnated with suitable materials effective to cause a color change therein when the fuse blows. Such impregnating materialsmay comprise easily oxidizable agents such as sodium or potassium chlorate either'with or without manganese dioxide, the fibrous materialbeing ignited and blackened when the fuse blows, 'or' the fibrous material 'orthe back face f the window or other appropriatepart visible therethrough such as the disk shown in'Figures l and?) and 11 inclusive may be treated with organic dies including vegetabledies which undergo color changes orbecome blackened when heated, or with inorganic pigments which may decompose or discolor whenheated. In the latter group may be mentioned metallic iodine which vaporizes when heated, mercurous carbonate which is normally yellow but becomes discolored when heated, and hydrated chromium chloride (CrClsfiHzo) which changes from a normally violet color when heated.

Figures 13 and 14 illustrate a further modification in which the two portions of the looped fuse element on opposite sides of the part of reduced cross section immediately back of the window are separated by a transverse insulating partition 6| of cardboard, fiber or the like, which acts to prevent excessive arcing when the fuse element blows, this decreasing the heat evolved and the amount of hot gases to be vented when the element blows.

From the foregoing description of certain embodiments of this invention, it should be evident to those skilled in the art that various other changes and modifications might be made without departing from the spirit or scope of this invention as defined by the appended claims.

We claim:

1. A device of the class described, comprising a non-conductive receptacle comprising a base and a glass top member having a cylindrical side wall portion and a closed end provided with a transparent window portion, a contact extending through said base, a conductive shell surrounding adjacent portions of said base and top member, and a fuse element secured at opposite ends to said shell and contact and having an intermediate portion positioned adjacent to and inwardly of said window portion, said base having an integral portion extending between said fuse element and said wall portion toward the end of said element secured to said shell.

2. A device of the class described, comprising a non-conductive receptacle including a base and a top, said top having a transparent window through its end, said base having a central contact extending therethrough, a conductive shell enclosing portions of said top and base, and a fuse element secured at one end to said contact within said receptacle, extending toward said window and then backwardly therefrom and between said base and top and secured at its opposite end to said shell, said base having a pair of integral radially spaced wall portions extending toward said window within said top between which said fuse element passes backwardly from said window toward its securement to said shell.

3. A device of the class described, comprising a non-conductive receptacle comprising a base and a glass top member having a cylindrical side wall portion and a closed end provided with a transparent window portion, a contact extending through said base, a conductive shell surrounding adjacent portions of said base and top member, and a fuse element secured at opposite ends to said contact and shell and having an intermediate portion positioned adjacent to and inwardly of said window portion, said base having an integral wall portion extending inwardly of said side wall portion toward said window portion and between said side wall portion and fuse element and having a perforation adjacent to the end of said side wall portion remote from said window portion through which and between said base and top member said element passes to said shell.

4. A device of the class described, comprising a non-conductive casing including a base and a glass top, said top having a cylindrical side wall portion and a closed end provided with a window portion, a conductive shell surrounding adjacent portions of said top and base, a contact extending through said base, said base having a pair of substantially concentric wall members extending within said side wall portion toward said window portion, and a fuse element secured at one end to said contact within said receptacle, extending within the inner of said wall members adjacent to and back of said window portion, and then turned back and between said wall members and through a perforation through the outer of said wall members and between said base and top and secured to said sleeve.

5. A device of the class described, comprising a receptacle having a window portion, a fuse element in said receptacle having a portion of reduced cross section opposite to said window portion, and a piece of non-conductive sheet material forming a background for said fuse element as viewed through said window portion, said sheet material having an opening therethrough back of said reduced cross section portion.

6. A device of the class described, comprising a receptacle having a window portion, a fuse element in said receptacle having a portion of reduced cross section opposite to said window portion, a piece of non-conductive sheet material forming a background for said fuse element as viewed through said window portion, said sheet material having an opening therethrough back of said reduced cross section portion, and material presenting a color different from that of said background positioned back of said opening and normally visible through said window portion adjacent to said reduced cross section portion, said last mentioned material being lightly secured for removal from said opening when said fuse element blows.

7. A device of the class described comprising a non-conductive receptacle having a base and a top, said top having a side wall and a closed end having a window portion, a conductive shell enclosing the adjacent portions of said base and top, a contact extending through said base, a fuse element in said receptacle secured at its ends to said contact and shell, respectively, and having an intermediate reduced cross section portion positioned back of and adjacent to said window portion, and a piece of sheet material positioned back of a portion of said fuse element and inwardly of said side wall and forming a background for said fuse element when viewed through said Window portion, said piece having a hole therethrough opposite to said reduced cross section portion.

8. A device of the class described, comprising a non-conductive receptacle having a base and a top, said top having a side wall and a closed end having a window portion, a conductive shell enclosing the adjacent portions of said base and top, a contact extending through said base, a fuse element in said receptacle secured at its ends to said contact and shell, respectively, and having an intermediate reduced cross section portion positioned back of and adjacent to said window portion, a piece of sheet material positioned back of a portion of said fuse element and inwardly of said side wall and forming a background for said fuse element when viewed through said window portion, said piece having a hole therethrough opposite to said reduced cross section portion, andbackground material of a difierent coloriromv said sheet material back of said opening and normally visible therethrough adjacent a window portion, a fuse element within said receptacle and having a portion extending across saidreceptacle back of and visiblethrough said window portion, and a piece of non-conductive sheet material back of saidifuse element portion and having an integral portion lying between said fuse element and said tubular side wall in position'to protect said side wall from breakage by impingement of not material thereagainst when said ,fuse element blows.

10. A device of the class describedcomprising a'receptaclehaving a glass top provided'witha tubular side wall :and a closed endpro-vided withea xwindow portion,-a fuse element-within saidre- *ceptacle andhaving a-portion extending across said receptacle back ofiandvisible throughzsaid window portion, and a disk of non-conductive material back of said fuseportion and havingan integral wing extension bendable into substantial conformitywith the inner face of said side wall and lying .betweensaid side walLand fuse element in position toprotect said side-wall from breakage by impingement of hot material thereon when saidfuse element blows. V V

' ALEXANDER :MILLER.

GEORGE GOODWIN. 

